Method of and apparatus for locating the direction of natural axes of quartz crystalsections



pr? 1948' G. w. WILLARD 2,439,836

METHOD OF AND APPARATUS FOR LOCATING THE DIRECTION OF NATURAL AXES OF A QUARTZ CRYSTAL SECTION Filed Sept. 9, 1943 3 Sheets-Sheet 1 lNl/ENTOR a. n1 WILLARD ArmkA/U 0F DISK 25 FIG. 2

April 2m 1948,. G; w. WILLAIRD 2 METHOD OF AND APPARATUS FOR LOCATING THE DIRECTION OF NATURAL AXES OF A QUARTZ CRYSTAL'SECTION Filed Sept. 9, 1943 5 Sheets-Sheet 2 m/vs/vm a. n4 W/LLARD Q ATTORNEY Apnl 20, 1948. .w wlLLARg 2,43%,836

METHOD OF AND APPARATUS FOR LOCATING THE DIRECTION OF NATURAL AXES OF A QUARTZ CRYSTAL SECTION Filed Sept. 9, 1943- 3 Sheets-Sheet 3 0N TENSION UP I63 0N TENS/ON M re'm/o/v up UP LHQ.

INVENTOR G. W WILLARD A TTORNEV Patented Apr.

MOD OF AND APPABAIIlS FOB LOCAT- ING THE DIRECTION OF NATURAL axes F QUARTZ CRYSTAL SECTIONS Gerald w. Willard, motto, u. 1., minor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York v Application September 9, 1943, Serial No. 501,019 3 Claims. (cl. ss-u) This invention relates to a method of and ap aratus for testing and particularly to a method :11 and apparatus fortesting quartz crystal secons.

An object of the invention is to facilitate the production of quartz piezoelectric plates.

A more specific object of the invention is to determine the direction in a section, slab or bar 7 of quartz of certain of the natural crystallogr phic axes thereof as .well as the electrical sense'of certain of the axes.

Still another specific object of the invention is to determine the sense (1-) of orientation of certain slabs or bars cut from a quartz mother crystal.

Yet another specific object of the invention is to determine the electrical sense of "1! cut quartz piezoelectric sections.

Raw quartz, from which quartz piezoelectric plates of the type now being used in increasing numbers in radio and other electrical circuits are produced, has, as is well known, three sets of crystallographic axes commonly known as the x or electrical axes, the Y or mechanical axes and the -Z or optical axis, respectively. The piezoelectric plates are cut from the raw quartz at various (but highly significant) orientations with respect to one or more of the natural axes. For example a plate may be cut from the raw quartz crystal so orientated that the major surfaces of the plate are parallel to an electrical axis of the crystal and inclined a definite amount and in the proper sense with respect to the optical axis. It will be apparent, therefore, that at certain points in the production of quartz piezoelectric plates it may become necessary to determine the direction and sense of certain of the natural axes of the .portion of quartz being used. Further, since two varieties of twinning, i. e., electrical and optical, are commonly foimd in quartz and since the twinning aifects the sense, but not the direction,

- of the crystallographic axes, it is also necessary during the cutting process to detect the twinning,

1r it'eidsts, and to' locate the boundaries between twins whereby the quartz piece to be cut may be marked 01! into separate homogeneous regions. The arrangement herein disclosed permits the ready detection of the presence of twinned regions and location of the boundaries thereof. After the performance of this step the arrangement of the present invention then permits the The arrangement of.the present invention, in one embodiment, permits the direction of the X axes of a "Z" out quartz section to be readily determined as well as the electrical sense (polarity) of each x axis. This information together .with

' a knowledge of the handedness of the portion (which also may be determined by use of the arransement herein disclosed) determine the direction and sense of angular displacement from the optical axis of plates to be cut therefrom.

In accordance with another embodiment, the

arrangement of the present invention permits the direction of the Z axis of an "X" cut quartzsection to be readily determined as well as the direction and sense, i. e., the angular displacement from the optical axis, of plates to be cut therefrom.

As used herein, "Z cut section" refers to a section so cut from the raw quartz crystal, commonly referred to as the "mother crystal that the major surfaces of the section are perpendicular to the Z axis of the crystal while X cut section" refers to a section so cut that the major surfaces are perpendicular to an x axis of the crystal. A section is ordinarily from V2 inch to 2 inches in thickness and is usually cut into sla (relatively thin portions whose thickness is somewhat greater than that of the desired finished plate) or bars" (relatively long and narrow portions whose smallest cross-section is somewhat greater than the milder face dimensions of the finished plate). The slabs are diced into the final wafers or plates while the bars are loafed or usable regions that are normally examined subdetermination, in oneregion at a time, of the directions and senses of axes or cuts to be made therefrom, or the sense of cuts already made to In accordance with a specific sequently' for direction and sense of crystallographic axes or desired cuts etc.

A feature of the present invention is the. location of a light diffusing element closely adjacent to an illuminated pin hole and remote from the actual primary source of light; the illuminated pinhole acts as a secondary source of light for the quartz specimens being examined. Y

Another feature of the invention resides in the provision of matching and marking arms which may be used in a cooperative manner in alignins and markins the crystal section.

embodiment of 2 r therefrom, or the electrical sense or optical handedness of quartz specimens.

the invention. a crystal section on table m tin: is provided having an aperture of pinhole dimensions passing therethrough. the rystal specimen tobeexaminedbeingsupportedonthetable over the pin hole aperture-h source of light is provided together with an optical system for conasserts indicate the direction 4 1 ofthe ofcut'forastandard crystal plate:

centra'ting the rays of l sht onto the lightdif by use oi'hydrofiuoric acid. As the observer.

views" the illuminated pin hole through the upper etched surface of the quartz section he will see a figure which appears to be located down in the section (as when looking at object under water). If the portion amined is untwinned, the figure will be, roughly, a three pointed star and its orientation on the section is definitely related to, and therefore will be an indication of, the direction and the sense of the three electrical axes of the section. Two viewof the section being ex-- 7 the event the etching process Fig. 14 shows the type of "mire" seen in a Z cut crystal section of ri ht-handed quarts in has been continued for a comparatively long periodbefore examination of the section:

Fig.15 shows the type of "figure" seen in the event-the section of Fig. 14 has been left-handed quartz:

Fig. 16 illustrates a hypothetical Z-cut section of quartz and shows the relationshipof the neures" to the sense of the X axes and to the hand- Fig. 17 is similar to Fig. 16 but shows the types or figures occurring when the etching process has been continued for a comparatively long period of time:

ing screens carried by flexible arms are provided (one for right-hand quartz and the other for left-hand quartz) and the proper screen is brought into position and the quartz section is rotated the requiredamount to bring the "figure" into alignment with guide lines provided on therespective screens. A marking template also carried by a flexible arm is next brought into position and the direction and sense oi. the electrical axes are marked on the section in accordance with guides provided by the template.

Complete understanding of the arrangement and operation of the devices contemplated by the present invention may be gained from consideration of the following detailed description and the accompanying drawings in which:

Fig. 1 is a side elevational view of an optical testing device embodying features of the present invention, a portion of the side walls being broken away to-reveal the interior arrangement;

Fig. 2 is a plan view of the device of Fig. 1:

Fig. 3 showsthe relative positions of the matching and marking arms of a first embodiment of the invention and shows the matching arm for one handedness of quartz in operative position;

' Fi 4 shows the marking arm of the first em- I bodiment of the invention;

Fig. 5 is a view similar to that of Fig. 3 except for the fact that the matching arm for the opposite handedness of ,quartz is shown in operative position; i

Fig. 6 shows the type or .figure" seen in a Z cut crystal section when examined in the apparatus of Fig. 1, the three guide lines of the matching arm being indicated by dotted lines:

Fig. 7 shows the section illustrated in Fig. 8 after rotation to bring the "figure" into alignment with the guide lines of the matching arm;

Fig. 8 shows the-crystal section after marking to indicate the X axes by use of the marking arm:

Fig. 9 is aview from below of the arm provided for holding the light diflusing element in position, the normal position of the element with respect to the aperture in the arm being indicated bydotted lines; i

Fig. 10 shows one marking armof a second emembodiment:

Figs. 18, 19 and 20 show alternative methods of mounting a specimenon the table; and

Fig. 21 shows the relationship between the different types of figures-" and the four possible diflerent types of twinning in an x cut quartz section.

Referring now to the drawings and first to Figs. 1 to 5, inclusive, there is illustrated a rectangular base plate i i upon which are mounted lamp housing II, which is a box-like enclosure, and lens and mirror assembly housing M, which is also a box-like. enclosure. Housing [4 is provided with a hinged cover which, when closed, forms a sloping support or table designated l5. It will be understood that base plate II, which is shown broken away, may be extended to support a power transformer or other associated equipment. Housinge i3 and ll, which are slightly separated so that the heat from the ventilated lamp housing it may be isolated from the optical housing ll, together form a substantially light'impervious optical system when table It is in closed position.

Fig. 12 shows the second marking arm of the second embodiment;

Fig. 13shows a crystal section after marking to ing bracket 42 tohcusing Three arms, matching arms 2i and 22 and marking arm 23, are mounted on table It, each arm being hinged and the relative positions of the three being such that any one may be swung downinto front or operative position while the other two are in rear or non-operative position wherein they do not interfere with the use of the operative arm; in Figs. 1, 2 and 5 arm 22 is shown in operative position; in Fig. 3 arm ii is shown in operative position and in Fig. 4 marking arm 23 is shown in operative position.

Aperture 24, which is of pin hole proportions,

is provided in the upper surface of table II; this small aperture is enlarged in the lower surface of the table sufiicientiy to contain disk 2!. Disk 25, which acts as a llghtdiifuser element, may comprise a disk of optical glass with an enameled face. (This is often referred to as flashed glass".) The enameled face of the disk is placed no.1. e.. toward the aperture :4. As shown in Fig. 1, the upper defining wall of the larger portion oi aperture 24 is tapered whereby only the peripheral portion of diffuser disk 25 iscontacted thereby and a space is left between the central surface of the disk and the aperture. This space serves two main purposes, first, it permits a wide angle oi illumination through the pin hole and, second, it provides a reservoir wherein dirt may accumulate so that the unit need be cleaned less frequently than would be the case otherwise.

- Lamp ii is mounted in lamp housing It, being supported by bracket 42. The two screws clampll pass through holes which are considerably oversize whereby the Zaxisandthesense assasss' bracket may be moved about to accurately focus lamp 4| with respect to pin hole aperture 24. The arrangement is such also that the lamp may be readily removed for cleaning or replacement. Bracket 42 is mounted in the upper portion of lamp housing It. the longer arm thereof extending out between lamp 4i and the ventilation hole in the top of the housing and acting as a light shield.

Lamp ll is provided with suitable conductors ningandtodeterminethedirectionoftheelec- 44 and 45 (shown in part only) for connection ts and as being held with convex surfaces toward each other. The lens assembly is normally held in the position illustrated in Fig. 1 by side strips 56 and all and two similar, but oppositely located, side strips that are not shown and by bottom strip H and a similar, oppositely located, bottom strip not shown. The assembly may be readily removed, however, by lifting it up out of the holding strips after first raising table I5; after removal of the lens assembly the outer surfaces of the lenses may be readily cleaned.

Light reflecting mirror 12 is angularly positioned in lens assembly. housing I4, being supported on bracket It and by strip It and a similar, but oppositely positioned, strip that is not shown. Stop member l5 mounted onthe lower edge of bracket It prevents the mirror from sliding downward along the surface of the bracket while spring member it normally prevents retraction of the mirror along the surface of the Ysupportlng bracket. However, the mirror may be readily removed for cleaning or replacement by first moving table it to open position and then pressing down the free end of spring 18 asuflicient amount to permit the mirror to clear the edge of the spring as it is retracted- Light difiusing disk 25 is normally held in the position illustrated in Fig. l, i. e., in the enlarged aperture beneath pin hole 24, by arm 8| which is rotatablyattached to the under surface of table i5 by screw 82. Arm BI is provided with aperture 83 which normally permits passage of light'to disk 2!. Aperture B8 is of slightly less '3- itbe assumed thatitisdesiredtoeheck'fortwintrical or x axes of a "Z" out piece-electric section and to determine the direction and sense of de-'- sired cuts. At least the upper surface of the section should first be prepared, for example, by grinding and etching or by etching alone in the instance of a sawn surface. (The etching process may utilize, for example, a 48 per cent hydrofluoric acid for aperiod of twenty minutes or a .weaker solution of the acid for a longer period or other well known fluorine'etching compounds). The section IBI to be tested is then placed in position on table II as shown in Real and 2 being located over aperture 24.

The examination for twinning and the markin of the'twinned regions, if any, are usually carried out at this point before the homogeneous usable regions are examined for axes. However, since the steps of the examination for twinning are more readily explainable after the orientation process has first been explained, it will be assumed for the moment that section IN is free of twinning. It will be assumed, further, that it has been determined by previous tests, that section II is left-handed quartz, and has been marked with two saw notches to indicate this handedness. (As used herein, "right-handedness" refers to quartz which when examined in the conoscope results in expanding optical rings when the conoscope eyepiece polarizing element is rotated clockwise while "left-handedness refers to quartz which under similar conditions results in contracting optical rings.) 7

It might be pointed out here that if the etching time referred to above be doubled the previous test for handedness will then be unnecessary as the iigures" obtained (to be described later) will also indicate the handedness.

Lamp II is now energized and the pair of lenses t5 and 4d and mirror 12 are effective to concentrate the resulting light rays through diffusing disk 25 and pin hole aperture 24. Matching arm diameter than disk 25 so that arm 8| when in normal position is eifective to hold the disk in position and yet has substantially .no blocking eirect thereon with respect to light rays. Arm 8| is normally held in the position illustrated in Fig. 1 through registry of pin 84 in an aperture provided in the under surface of table It. Arm

sl may be rotated about screw 22 on occasion. however, by first pulling down the free end of the arm sufliciently to disengage pin 84 from the aperture, whereby disk 25 may be readily removed and any dirt or quartz particles which may have fallen through aperture 24 cleaned away.

It will be clear from the above description that the various parts of the particularly the diffusing disk. the pair of foeussing lenses and the reflecting mirror, are all readily removable for cleaning and rt.

In order to further describe the 22 (the snatching arm for use with left-handed quartz, which has been marked with two notches to indicate use of the number-"2""arm) is now swung down into operative position over section Ifii (as shown in Fig. 2). It might be pointed out here that arm 22, and the other matchingv and marking arms, are comprised, at least for a portion of their length, of flexible material so that the free end of the arm may be brought into close engagement with the upper surface of the crystal section regardless of the thickness thereof.

An aperture, I02, is provided in arm 22 near the free end thereof. Plate I (Fig. 1), which is provided with an aperture similar to aperture I02, is attached to the free end of arm 22 by four screws or other suitable means, being so positioned that the aperture in the plate is in registry with aperture I02. Matching plate I04. which is of suitable transparent material, is clamped between plate I" and the end of arm 22. Plate I04 is provided with three properly oriented guide lines I05, I and III which radiates from a common center point at intervals of degrees. Plate I04 is so positioned that the common center point of the three guide lines coincides-with the center of aperture I02, the center of the aperture in plate Ill and pin hole 24. The assembly provided at the free end of matching arm 22 might well be referred to therefore as a matching guide.

Now as the observer peers down through the invention. let :6 apertured end of arm 22 (the arm, as

be compared, roughly, to a three-pointed star or to an equilateral triangle in shape and which will appear to be located between the upper surface of section I ll and the pin hole itself. (Observ- 8 arm 22 and that, otherwise, the test would have been carried out as described. The arrangement ofmatchingarmlbincludingtheassemblyofthe ance of this general type of "figure" is referred to in a bound booklet by Armand de Gramont, "Recherches sur le Quartz Piezoelectric." Paris Ed. de la Rev. DOpt. 1935.) Upon detecting the "figure," the observer then checks the align ment of its three .lengths" or axes with guide lines Ill, ill and Ill. One of the many possible results of the check is indicated in Fig. 8 where it wil be seen the "figure" is misaligned with respect to the guide lines. The observer now rotates section III until he brings the "figure into substantial coincidence with guide lines III, I and I01, that is with the guide lines substantiaily as; blsectors of the respective apices of the figure. This position is indicated in Fig. 7.

Now that section IIII has been orientated properly on table II, the observer swings matching arm 22 back out of the way and brings marking arm 23 down into operative position over section III. The marking arm is similar, generally, to matching arm 22 but differs therefrom in that a plate III is attached to the free end thereof by means of three screws, or other suitable fastening means. Plate III is provided with a properly oriented Y-shaped cut-out template or marking guide 2, in which the three guide lines are again 120 degrees apart.

The observer new places the point of a pencil or other suitable marking stylus in cut-out template I I2 and marks the outline thereof on the surface of quartz section Ill. The section so -marked is shown in Fig. 8. It is known to the observer that the respective X axes are parallel to the marked lines and he knows therefore that certain plates, for example, the BT cut plate, may be cut parallel to any one of the lines. (The BT cut plate as disclosed in Patent 2,218,235. issued V to me on October 15, 1940 is produced by so cutting the plate with respect to the axes of the crystal that the principal faces of the plate are parallel to an x axis of the crystal and are ori-' ented or inclined at an angle of approximately- 49 degrees with respect to the Z axis.

While the. orientation of the figure or pattern seen in the quartz section is, as stated, an indication of the direction of the X axes and said axes are located with reference to the apices of said figure, they do not exactly coincide .with the apices but are slightly to one side. That is. the figure is rotated a slight, but definite. amount (of the order of degrees to degrees) away from the true direction of the X axes of the section, this rotation being in a clockwise direction for left-hand quartz and in a counter-clockwise direction for right-hand quartz. The orientation of the guide lines on matching arm 22 with respect to that of the marking guide on the marking arm and the orientation of the guide lines on matching arm II with respect to said marking guide are such as. to compensate exactly for the .error" between the figure and the true direction of the X axes in left-hand quartz and right-hand quartz respectively.

It will be understood that, in the above example, had the quartz section being examined been right-handed quartz (and marked so by one saw notch), matching arm 2| (bearing the numeral "1) would have been used instead of matching matching guide, is arm I2.

Now all In the event that the etching process be continued for a longer period, as noted above, in order that an indication of handedness may be obtained, the figure seen in the Z out section will then be as shown either in Fig. 14 or Fig. 15. The "figure of Fig. 14 is that obtained if the "swirls" while the "figure" of Fig. 15 is that obtained ii the quartz is left-handed and shows counter-clockwise "swirls."

If this method of determining the handedness of the quartz which involves the more developed "figures is to be followed, then the designations 1" and "2 on arms 2| and 22 respectively may well be replaced by a copy of the respective figur shown in Figs. 14 and 15.

The alignment of the swirl figures" with the guide lines of the matching arms is exactly the same as that described above with reference to Figs. 6 and '1 except for the fact that we neglect the "swirl" portions oi the "figure" when aligning.

Considering now the use of the arrangement for detecting twinning as mentioned briefly above, it might be pointed out first that the figure of Figs. 6 and 7 is not identically aligned with the x axes of the quartz section. Actually the "figures are out of alignment with respect to the X axes by 10 degrees to 15 degrees and their sense and sense of misalignment are related to the sense of electric axes and to the handedness of the quartz as shown in Fig. '16. There is illustrated in Fig. 16, a hypothetical section of quartz in which there are four diiferent regions exhibiting the four possible variations of electric sense and handedness that might be simultaneously exhibited in a twinned quartz section. In all cases the electrical axes of each portion are parallel to those of another portion but may be of opposite sense. As here illustrated the respective arrow point ends of the axes are the ends which would be electrically positive by tension. 1

The section illustrated in Fig. 17 is similar to that of Fig. 16 except that in this instance the etching process has been continued for a longer P riod as discussed above in order that "swirl figures may be produced.

Now it will be clear that if a section such as that shown in Fig. 16 or 17 be placed on table II with a boundary of any two different regions directly over pin hole 2, the observer would then see parts of two diil'erent "figures" instead of a single figure. Twinning is easily detected if present in a section, therefore, by shifting the section about on table II with respect to pin hole fl and observingwhether or notanymixed figures" occur. Actually the boundary line itself similar to that of matchinl willstandoutcleariyandmeybetracedonthe surfaceofthesectionwithapencilorother for twinning in order to note whether, twinning.

boundaries go approximately straight through the section or whether they sllllt oil! to a side of the section.

After the inspection for twinning and alter the twinned regions, it any. have been marked. all usable regions may then be tested for direction of axes and sense of cut as outlined above.

Applicant has determined that the size of the flgure" seen is. proportional to the thickness of the crystal section and that, when the flgure" is small as with very thin quartz sections, larger "flgures may be obtained by placing a thick piece 01' plate glass on the table under the crystal section. In such event, however, it is necessary to polish the under-side of the section or. more simply,.to wet it with a liquid having a-refractive index matching that of quartz, for example, between 1.53 and 1.56. Fig. 18 illustrates a relatively thin quartz section iii supported over aperture 24 of table it by a relatively thick piece of plate glass I52.

If desired, section lbi may, as shown in Fig.

19, be immersed in a liquid, which has a refractive index matching that of quartz, in a glass vessel Hit and the vessel positioned over the pin hole aperture in table it. This latter method is particularly applicable in connection with sections which have only one flat top surface; Fig. 20 shows such a section in in position for testing. In addition to the obvious advantageous features of the arrangement described such as accessibility and removability oi the various parts, compactness, absence of complicated moving parts, adaptability to comfortable bench use from a sitting position and adaptability to accurate use by unexperienced persons, particular attention is directed to the novel arrangement Y whereby the light diflusing element (disk 25) is placed under and directly adjacent to the pin hole (aperture 24) and at a distance from the light source 4 I. Considerable and important advantages result from locating the light diffusing element adjacent to the pin hole rather than cating it at a distance from the aperture as has been the practice heretofore; one arrangement proposed heretofore, for example, involved utilizing the coated surface of the light source bulb itself as the diiiusing element. With the light diffuser located adjacent to the pin hole as contemplated by the present invention, preparation of the under surface of the quartz section to be eramined is quite. unimportant and it may be ground, polished, etched or oiled as convenient and as incidental to the grinding and etching treatment usually applied to the upper surface of the section or it may be mounted in a glass dish of oil or other suitable liquid. Further, with this novelarrangement a concentrated beam of light is sent through the pin hole and strong figures are seen even under daylight" working conditions.

In addition to use in determining and marking the direction of the X axes and direction and 'an "x"-cut quartz section and the sense of the angular cuts to .be made from these sections.

For such use a diiferent set of matching and marking arms is used, the arms of this set bein illustrated in F188. 10, 11 and 12.

In order to illustrate the operation of the arrangement for this latter pu pose let us assume that "1:" cut quartz section ill be placed on table It and matching arm iii brought down into operative position thereover as shown in Fig. 11. It will be assumed that at least'the upper surface of the section has first been prepared, for example, by grinding and etching or by etching alone as referred to above. Ann I is provided at its free end with window In of suitable transparent material; two parallel lines I" and I are provided on this transparent material. This arrangement may well be referred to as a match- 2 ing guide.

, window I32 he will see a "flgure in section MM Now as the operator, using the testing arrangement inthe samegeneral manner as described in detail above, peers down through The figure in this instance, however, will not be the same as those described above as seen in the z cut section but will be similar to one of the four figures it, it, Ill, Iii, which are reproduced on matching arm iti as guides.

It will be noticed that. while the parallelo- Bram" figures-island i8! and the H 'flgures it and MI, respectively, are of generally similar outline, they are mirror images and are easily distinguishable one from the other. Figures lit and I are easily distinguishable due to the fact that the longer angular toes" extend in respectively' different directions as do the respective pairs of tilted parallel lines while figures W5 and iii are distinguishable due to the fact that the respective "high sides are oppositely positioned. It might be noted that such figures are obtained, for example, by etching in 48 per cent hydrofluoric acid for to so minutes, but that ii the etching is continued for hours the appearance of the figures changes completely through addition of new lines to the figure as well as through loss of some of the lines here shown.

Assuming now that a flgure" similar to either I35 or I38 is seen, the two arrows provided on matchingarm :i3l indicate that the right-hand marking arm, 1. e., marking arm I42, (Fig. 12)

should be used in this particular case. The two longer, vertical sides or the figure are first lined up with lines I33 and I" of matching arm l3! by rotating crystal section I after which matching arm IN is swung back out of the way and marking arm It! is brought down into operative position over crystal section I" as shown in Fig. 12. Using edge It! of the marking arm as aguide a line is then marked on crystal section I30 with a pencil or other suitable marking stylus. This line (line I of Fig. 13) indicates the direction of the optic or Z axis of the quartz crystal. Using cutout portion I45 as a template or marking guide a second line (line I. of Fig. 13) may be drawn on the crystal section, this line indicating the sense, or direction. of the angular cuts to be made from the section. The angleof the cut-out portion provided on the matching arm will be in accordance with the particular cut of the plates to be produced from the section. In the present instance it is assumed that plates of the type.

sense of cuts from a "Z cut section, the arrange-i lo commonly referred to as BT cuts are to be pro-' ll duced: this plate as mentioned above is disclosed in Patent 2,218,225 issued to moon October 15, 1940, and is produced by so cutting the plate with respectto the axes of-the mother crystal that the principal faces of the plate are parallel to an x assasae stood that for other standard cuts, wherein the orientation difiers from that of the or cut referred to, the angular position of the cut-out portions may be varied accordingly, or the orientaplate or other shape of crystalline specimen (so long as it has at least one plane surface) of any orientation with respect to the crystallographic axis, for determining the direction and sense of.

crystallographic axes or preferred cuts or for detecting and marking twinned regions and the embodiments described should be takenas illustrative of the invention and not as restrictive thereof.

What is claimed is:

1. The method of locating the direction of one of the natural axes of a quartz crystal section that has been so cut from the mother crystal tion may even be determined from the above marking.

It will be understood that, in the aboveinstance, had either figure I" or III been seen in section Ill. then the left-hand marking arm (arm I", Fig. 10) would have been used as the arrows associated with figures I" and Ill point 'to the left. If section I 80 had been twinned (a fact which, of course. would have been previously determined as in the instance of section III) parts of the two figures shown in Fig. 11 would have been Joined. Fig. 21 illustrates the actual relationship of four possible "figures to the four possible conditions of twinning in an x cut section I". It will be observed that the respective sides of the "H- shaped figures" are misaligned with respect to the Z axis by 4 degrees and thatthc respective sides of the "parallelogram figures" are misaligned with respect to the Z axis by 7 degrees: the average, degrees, is the inclination of the Z axis guide line ill of arm 2 (Fig. 12) and the similar guide line of arm I" (Hg. 10). It might be noted at this point also that in an x out section. such as Ill. when one surface is electrically positive the opposite surface is negative and that the H-shaped figure" always occurs with the positive face and the "parallelogram shaped figure always occurs with the negative face as in Fig. 21.

It will be clear from Fig. 21 and from previous description above that the embodiment of Figs. 10, 11 and 12 may bound for detecting and marking optical twinning and electrical sense of X cut quartz sections as well as of out.-

While certain specific embodiments of the invention have been'selected for illustration and detailed .description, the invention is not, of course, limited in its application'to these embodiments. For example quartz crystal cuts other direction and sense than those specifically referred to ay b ex mined as well as crystalline materials other than quartz. Further, the arrangement might be used in connection with study of the surface texture of manufactured transparent articles to determine proper surfacing operations In applying the method to unknown cuts or crystals-it is necessary only to determine the type of ffigure" that is given by the particular specimen, to relate this figure to the predetermined crystallographic axes of the specimen and, with this knowledge, to

then examine "figures" in other specimens to de-.

tcrmine the axial relations. The surface of the specimen-may be "prepared? in other ways than by etching, for example, it hasbeen foundthat good figures may be obtained if the surface of the specimen is prepared by grinding. The arrangements contemplated may he used for ex-' amination of any type of section, bar, slab. wafer.

that at least one of the maJor surfaces 01' the section is perpendicular to a predetermined one of the natural axes of the crystal which comprises the steps of etching one of the major sur.. faces of the section. directing light successively through a light diffusing element, an aperture of pin hole magnitude and the other of the major surfaces of the section to produce a figure in the quartz section of definite configuration the orientation of which is difinitely related to the direction of said one of the natural axes of the crystal section in that it is rotated a definite amount away from the direction of said one axis, observing thefigure through the etched surface of the "section, moving a matching guide having a plumoving said matching guide to a position out of contact with the surface of the quartz section and removed from the first-mentioned position, and moving a marking guide to a predetermined position in contact with a surface or the orientated section and coaxial with the light diffusing element and the aperture, said marking guide having a straight guiding edge, and utilizing said guiding edge of said marking guide and cooperating marking means to mark a line indicating the direction of the desired natural axis on the etched surface of the section, said matching guide and said marking guide being so orientated with respect to each other when in said respective predetermined positions as to compensate for said rotation of said figure with respect to the direction of said one axis, the compensation resulting in coincidence between the direction of said guiding edge and the true direction of said one axis.

2. The method of locating the direction of the x axes of a quartz section that has been so cut from the mother crystal that the major surfaces thereof are at right angles to the Z axis of the crystal which comprises illuminating the section to produce an optical pattern of triangular shape the orientation of which is definitely related to the direction of the x axes of said section in that it is rotated a slight. definite amount away from the true direction of said x axes, moving a matching guide to a predetermined position above said section, said matching guide bearing three straight aligning guide lines radiating from a common center point at intervals of degrees, viewing said pattern through the portion of said matching guide which bears said aligning guide lines. rotating said section to cause each of the guide lines of said matching guide to be substantially coincident with a bisector of the respective angles of the triangular pattern, moving a marking guide to a predetermined position over said section, said marking guide bearing a slotted star pattern, and marking the direction of the X axes of said section by drawing lines with a suitable stylus projected through said star pattern, said star pattern and said aligning guide lines when the respective guide is in its said predetermined position having such relative angular displacement as to compensate for the angular difierence between said bisectors and the true direction of the X axes, the compensation resulting in coincidence between the direction of the slots in the star pattern and the true direction of the X axes.

3. An optical device for locating and marking the X axes of a quartz crystal section that has been so cut from the mother crystal that the major surfaces of said section are at right angles to the Z axis of the crystal comprising an opaque Plate having an aperture therein over which the crystal section can be placed and having a source of illumination behind the crystal section suitable for passing a beam of light into the lower face of the crystal section whereby to produce therein the usual characteristic triangular light pattern as viewed from the upper face of the crystal section, means for mounting said crystal section to be rotatable, the light pattern also rotating therewith, a pair of guide plates fixedly se-' cured to said device and each constrained to move in a definite path whereby to bring said guide plates one at a time into the same position of registry with said crystal section above said section, the first of said guide plates having three guide lines meeting at a common point and diverging at angles of 120 degrees from one another to serve when in said position of registry as lines of reference of the optical axes of said section when the latter is rotated by the observer to bring said light pattern into an orientation at which said guide lines appear to bisect the, apex angles of the light pattern, and the second of said guide plates having three slots therein in star configuration in such angular displacement, when said second plate is in its respective position of registry, from said lines of reference as to serve as a ruling guide for marking on the upper face of said crystal section the angular position or the X axes thereof.

GERALD w. WILLARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,157,437 Shipley May 9, 1939 2,218,489 Gerber Oct. 15, 1940 30 2,313,143 Gerber Mar. 9, 1943 

